The invention relates to an interconnector for a fuel cell stack and to a method for production.
A high-temperature fuel cell converts the chemical energy of a fuel, such as hydrogen or methane, directly into chemical energy. To this end, the fuel is oxidized using an oxidizing agent, such as air or pure oxygen. The fuel and oxidizing agent are separated by an oxygen ion-conducting solid electrolyte, such as yttrium-stabilized zirconium oxide.
The electrolyte is coated with porous, catalytically acting electrode materials. In general, the anode on the fuel side is made of a cermet of metallic nickel and zirconium oxide. The cathode on the oxidizing agent side is typically made of perovskite, based on lanthanum.
Since an individual fuel cell only supplies a very low voltage, for technical applications, a plurality of cells must be interconnected in a fuel cell stack. To this end, a gas-tight, yet electrically conductive interconnector is disposed between two fuel cells. The interconnector must have a thermal coefficient of expansion between 10×10−6 and 12×10−6 K−1 that is suited to the remaining components of the fuel cells. In addition, it must not oxidize in the operating atmospheres for the fuel cell.
In principle, ferritic chromium steels meet these requirements. However, contacting the anode with such an interconnector is problematic. The protective oxide layer formed by these materials drastically reduces the electrical conductivity of the interconnector. Furthermore, nickeliferous means are typically used for the electrical contact between the interconnector and the anode. If these means are in direct contact with the interconnector, both these means and the interconnector disadvantageously degrade after only a relatively short operating period.